Improving the rheological performance of cement-based materials via pre-carbonated cement slurry

Pre-carbonation treatment demonstrates strong potential for simultaneously enhancing carbonation efficiency and optimizing the rheological performance of cement-based materials. However, the coupled influence of carbonation duration and water-to-cement (w/c) ratio on rheological evolution remains underexplored, hindering systematic application in additive manufacturing. This study employed rheological modeling, compressive strength testing, microstructural characterization (XRD, TGA, SEM), and in situ thermal monitoring to evaluate the effects of carbonation duration (0-40 min) and water-to-cement ratios (0.4/0.5). Results revealed that dynamic viscosity increased linearly with carbonation duration (R-2 = 0.96) and decreased with higher w/c ratios, confirming the feasibility of rheological control through parameter tuning. Early compressive strength was enhanced by 20 % without compromising long-term stability (28-day strength variance <3 %). Micro-structural analysis showed a 301 % increase in calcite content in 40-min carbonated specimens and the in-situ formation of submicron CaCO3 particles. These particles improved rheological behavior through dual mechanisms: reducing free water film thickness and increasing interparticle friction, while also decreasing the effective lubrication volume via particle agglomeration-induced water entrapment. The findings establish a theoretical and practical foundation for applying pre-carbonation in 3D printing and shotcrete systems that require precise rheological tailoring, promoting the integration of low-carbon construction materials with advanced additive manufacturing technologies.